1. Field of the Invention
The present invention relates to a system for studying, identifying and characterizing the temperature gradients within a volume of water.
2. Description of the Prior Art
Typically, the bandwidth of the spatial variability of a thermal plume generated by a small cylindrical heating element is much greater than the bandwidth of available transducers. Since the scattering associated with the thermally driven buoyant plume is well described by weak scattering theory, the Bragg scattering condition can be applied. This condition allows for a more fully resolved spatial bandwidth of the scattering volume by aligning multiple source/receiver pairs of acoustic transducers in a common scattering direction. To properly study this problem, the source/receiver pairs of transducers must be located at a known distance from the area to be studied and also must be aligned at a specific angle with respect to each other and the overall coordinate system.
In the laboratory, the problem was studied using ultrasonic transducers mounted on search tubes. A Compumotor multi-axis positioning system was used to identify the location of the search tubes, which were then suspended from a track transversing the top of the test tank. A stainless steel J-type support frame, which was secured to the tank by an array of clamps and rods, held a small cylindrical heating element at its base which was used to generate turbulence. The heater was powered by a Variac in order to control the nature of the turbulence.
This arrangement had many drawbacks including long set-up time, high degree of inaccuracy of alignment with the heating element and other transducers and very low degree of repeatability. The maximum number of transducers which could be aligned for an experiment within a reasonable set-up time was four. Another problem specific to the search tubes was the separation of the UHF connector from the body of the ultrasonic transducer due to installation and removal of the transducers to and from the search tubes.
Other arrangements for supporting acoustic transducers and hydrophones in an underwater environment are known in the art. For example, U.S. Pat. No. 4,007,436 to McMahon illustrates a self-deploying instrument assembly which includes a plurality of hydrophones mounted on a flexible sheet. The assembly further includes a series of resilient rods which extend from one side of the sheet from positions spaced around the periphery thereof to a hub. The resilient rods are deflectable laterally inwardly with consequent folding of the sheet to place the assembly in a storable configuration smaller than its normal operative configuration.
U.S. Pat. No. 4,576,034 to Ferree et al. illustrates an apparatus for calibrating an ultrasonic transducer array by moving it along an arcuate calibration test member. The apparatus includes four upright posts interconnected by a rectangular carriage which is slidably movable vertically along the posts. A horizontal pivot shaft is rotatably mounted on the carriage. Fixed to the shaft and depending therefrom are two pendulum arms, interconnected at their lower ends by a pair of cross bars on which is slidably mounted a mounting block. An attachment rod is vertically slidably movable in the mounting block and carries a coupling joint at its lower end for mounting the transducer array. A reversible gearmotor drives the pivot shaft through a chain and sprocket assembly in an oscillating motion. Backlash in the gear train is reduced by a bias weight.
U.S. Pat. No. 5,412,622 to Pauer et al. illustrates an apparatus including a plurality of omnidirectional hydrophone sensors in a particularly configured array comprised of ring members which are carried between a plurality of tensioned cables. The cables are tensioned by an anchor weight at the bottom end of the array and a capsule float at the top end. The configuration facilitates simplified signal processing techniques to achieve sound source discrimination in both azimuth and elevation within an underwater environment.
None of these patented underwater support systems lend themselves to the study, identification and characterization of the temperature gradients within a volume of water.